ESR spectra of the MnO, MnO2, MnO3, and MnO4 molecules at 4 °K

Abstract

The molecules MnO, MnO2, MnO3, and MnO4 have been prepared by the vaporization and reaction of manganese atoms with O2, N2O, or O3 and isolated in various inert-gas matrices at 4 °K. ESR has been used to determine magnetic parameters which are interpreted in terms of molecular geometry and electronic structure. MnO is confirmed to have a σπ2δ2, 6Σ+ ground state with g⊥=1.990(7) (assuming g∥=ge) and a zero-field splitting in accord with the gas phase value ‖D‖=1.32 cm−1. Hyperfine splittings due to the 55Mn (I=5/2) nucleus are ‖A∥‖=176(8) and ‖A⊥‖=440(11) MHz. MnO2 is a linear 4Σ− molecule with probable configuration σδ2, ‖D‖=1.13 cm−1 (assuming g∥=g⊥=2.0023), ‖A∥‖=353(11), ‖A⊥‖=731(11) MHz. MnO3 exhibits very large hf splittings ‖A∥‖=1772(3) and ‖A⊥‖=1532(3) MHz indicative of a sdz2 hybrid 2A1 ground state of D3h symmetry. The spectrum of MnO4 is consistent with a C3v molecule distorted from a 2T1 electronic state in tetrahedral symmetry by a static Jahn–Teller effect. g and A tensors are slightly anisotropic: g∥=2.0108(8), g⊥=2.0097(8), ‖A∥‖=252(3), ‖A⊥‖=196(3) MHz. The electron hole is almost entirely in an oxygen π-bonded orbital with one oxygen atom displaced along its Mn–O bond axis.